Abstract

Alagille syndrome is a rare disorder commonly associated with pulmonary artery stenosis. Studies exist discussing the cardiovascular sequela but no consistent phenotype, or pattern of pulmonary artery stenosis, has been described.The objective of this study was to characterize the distribution and severity of pulmonary artery stenosis in patients with Alagille syndrome based on computed tomography angiography.A retrospective chart review identified patients with Alagille syndrome who had undergone CT angiography. Pulmonary trunk (MPA), left main pulmonary artery (LPA) and right main pulmonary artery (RPA) diameters in Alagille patients were compared with those from matched control subjects. Stenoses at lobar and segmental pulmonary arteries were categorized as: Grade 1 (<33% stenosis), Grade 2 (33-66% stenosis) or Grade 3 (>66% stenosis). Involvement among the different lung regions was then compared.Fifteen patients ages 6 months to 17 years were identified; one had surgical augmentation of the central pulmonary arteries and was excluded from the central (main, right and left) pulmonary artery analysis. The proximal LPA and RPA, but not the MPA, were significantly smaller than those of the control subjects (P<0.01). The proximal LPA was significantly smaller than the proximal RPA (P<0.01) in the Alagille group (0.55 LPA:RPA ratio). Within the Alagille group, 75% of the lobar and segmental branches showed mild or no stenoses (Grade 1), 17% showed moderate stenosis (Grade 2) and 8% showed severe stenosis (Grade 3). While not statistically significant, the right lung demonstrated a greater percentage of Grades 2 and 3 stenoses (28%, right vs. 20% left, P=0.1). The right middle and lingula lobes of both lungs showed more Grade 2 and 3 stenoses (33% upper/middle vs. 18% lower, P<0.01).We describe a common pattern pulmonary artery stenosis in Alagille patients consisting of severe proximal LPA stenosis, heavy involvement of the lobar and segmental branches (more often right than left), and a greater involvement of the upper lobes. Knowledge of this phenotypic pattern can help in the diagnosis of Alagille syndrome in patients presenting with pulmonary artery stenosis.

Abstract

Patients with tetralogy of Fallot, pulmonary atresia, and major aortopulmonary collaterals (TOF/PA/MAPCAs) undergoing unifocalization surgery are at risk for prolonged postoperative respiratory failure. We sought to understand whether patients undergoing reconstruction and incorporation of occluded pulmonary arterial branches were at risk for worse postoperative outcomes.We performed a retrospective chart review to identify patients who underwent unifocalization or unifocalization revision with incorporation of occluded pulmonary artery branches. Patients with and without occluded branches were compared, with a focus on clinical outcomes.We studied 92 patients who underwent unifocalization procedures between 2010 and 2014, 17 (18%) of whom underwent reconstruction of occluded pulmonary artery branches. Patients with occluded vessels were more likely to require staged unifocalization procedures, although more than two thirds of this cohort eventually underwent complete intracardiac repair. Durations of mechanical ventilation, intensive care, hospital stay, and the need for early reoperation were similar between the two groups.Occluded pulmonary arterial branches can be safely recruited into the pulmonary vasculature in patients with TOF/PA/MAPCAs without a significant difference in postoperative outcomes compared with patients who did not have an occluded branch. Incorporation of occluded branches may also facilitate ultimate complete intracardiac repair in this complex population of patients.

Abstract

Anomalous aortic origin of a coronary artery (AAOCA) has been associated with myocardial ischemia and sudden death. The past decade has provided important insights into the natural history and typical patterns of presentation. However, there are also a number of unresolved controversies regarding the indications for surgery and the efficacy of that surgery. The purpose of this study was to review our surgical experience with AAOCA in 115 patients at a single institution.One hundred and fifteen patients have undergone surgical repair of AAOCA at our institution. There were 82 males and 33 females, and the median age at surgery was 16 years. Fifty-nine patients had preoperative symptoms of myocardial ischemia, including 56 with exertional chest pain or syncope and 3 sudden death events. Twenty-four patients had associated congenital heart defects. Seven patients had an associated myocardial bridge.Surgical repair was accomplished by unroofing of an intramural coronary in 86, reimplantation in 9, and pulmonary artery translocation in 20. There has been no early or late mortality. Fifty-seven (97%) of the 59 symptomatic patients have been free of any cardiac symptoms postoperatively. Two patients had recurrent symptoms and underwent reoperation (one had revision of the initial repair and one had repair of a myocardial bridge).Surgical repair of AAOCA can be safely performed and is highly efficacious in relieving symptoms of myocardial ischemia. The two "surgical failures" in this series had an anatomic basis and underscore the need to reassess both the proximal and distal anatomy in these patients.

Abstract

Anomalous aortic origin of the left coronary artery is rare and confers increased risk of sudden cardiac death. Accurate diagnosis is crucial and often requires many diagnostic modalities. This case report highlights the echocardiographic characteristics and pitfalls in diagnosing the anomaly in addition to the advantages of using computed tomography and magnetic resonance imaging in a pediatric patient.

Abstract

Cardiac C-arm computed tomography (CT) uses a standard C-arm fluoroscopy system rotating around the patient to provide CT-like images during interventional procedures without moving the patient to a conventional CT scanner. We hypothesized that C-arm CT can be used to visualize and quantify the size of perfusion defects and late enhancement resulting from a myocardial infarction (MI) using contrast-enhanced techniques similar to previous CT and magnetic resonance imaging studies.A balloon occlusion followed by reperfusion in a coronary artery was used to study acute and subacute MI in 12 swine. Electrocardiographically gated C-arm CT images were acquired the day of infarct creation (n = 6) or 4 weeks after infarct creation (n = 6). The images were acquired immediately after contrast injection, then at 1 minute, and every 5 minutes up to 30 minutes with no additional contrast. The volume of the infarct as measured on C-arm CT was compared against pathology.The volume of acute MI, visualized as a combined region of hyperenhancement with a hypoenhanced core, correlated well with pathologic staining (concordance correlation, 0.89; P < 0.0001; mean [SD] difference, 0.67 [2.98]?cm). The volume of subacute MI, visualized as a region of hyperenhancement, correlated well with pathologic staining at imaging times 5 to 15 minutes after contrast injection (concordance correlation, 0.82; P < 0.001; mean difference, -0.64 [1.94]?cm).C-arm CT visualization of acute and subacute MI is possible in a porcine model, but improvement in the imaging technique is important before clinical use. Visualization of MI in the catheterization laboratory may be possible and could provide 3-dimensional images for guidance during interventional procedures.

Abstract

Most cardiac diseases in the newborn are caused by structural abnormalities developed in utero. With few exceptions, palliative and definitive treatments require cardiac surgery. The diagnosis and management decisions regarding uncomplicated lesions, such as atrial septal defect, ventricular septal defect, patent ductus arteriosus, and tetralogy of Fallot, can be accomplished by echocardiography alone. Abnormalities beyond the sonographic window, complex 3-dimensional lesions, and detailed functional information require additional imaging. In the past, this was fulfilled by catheter angiography, but today much of the information can be obtained from noninvasive computed tomography angiography and magnetic resonance imaging. This article discusses the design and application of these imaging techniques to the newborn, with emphasis on safety, efficacy, and image quality. Understanding the capabilities and limitations of these techniques is crucial for making rational choices among imaging options based on sound risk and benefit considerations. Important examples of congenital heart lesions have been illustrated with 3-dimensional reconstruction from computed tomography and magnetic resonance images.

Abstract

In this study, with the use of computational fluid dynamics, we evaluate the postoperative hemodynamic performance of the first cohort of patients undergoing a handcrafted Y-graft Fontan procedure and validate simulation predictions of hepatic blood flow distribution against in vivo clinical data.An 18-12 × 2-mm handcrafted Y-graft modification of the Fontan procedure was performed in 6 patients. Early (at the time of discharge) and 6-month postoperative 3-dimensional magnetic resonance imaging data were collected. Patient-specific models were constructed for flow simulations.Hepatic blood flow distribution varied among patients. Lung perfusion data (n = 3) showed good agreement with simulations. Postoperative asymmetry in hepatic blood flow distribution was reduced 6 months postoperatively. In 1 patient, low wall shear stress was found in the left limb of the Y-graft, corresponding to the location of subsequent thrombosis in the patient.The credibility and accuracy of simulation-based predictions of postoperative hepatic flow distribution for the Fontan surgery have been validated by in vivo lung perfusion data. The performance of the Y-graft design is highly patient-specific. The anastomosis location is likely the most important factor influencing hepatic blood flow distribution. Although the development of thrombosis is multifactorial, the occurrence in 1 patient suggests that simulations should not solely consider the hepatic blood flow distribution but also aim to avoid low wall shear stress in the limbs.

Abstract

To demonstrate the technical feasibility and describe intermediate outcomes for the initial patients undergoing handcrafted, area-preserving, Y-graft modification of the Fontan procedure.A retrospective review of a pilot study was undertaken to describe preoperative, intraoperative, and postoperative results.Six patients underwent successful procedures and remain alive 3 to 4 years later. The median age at operation was 3.3 years, and median weight was 13.2 kg. Five operations were done without cardiopulmonary bypass and no intraoperative pressure gradients were found. Five patients were extubated by postoperative day 1, Fontan pressures were 12 to 14 mm Hg, transpulmonary gradients were 6 to 8 mm Hg, and no renal or hepatic function abnormalities were found. Length of stay was 10 to 64 days. One patient required venovenous extracorporeal membrane oxygenation for previously undiagnosed plastic bronchitis (64-day stay); another required reoperation for an incidentally diagnosed aortic thrombus (44-day stay). One patient had occlusion of a Y-graft limb noted on magnetic resonance imaging follow-up at 3 months. Catheterization showed excellent hemodynamic parameters and no Fontan obstruction. Occlusion was believed to be due to right-sided pulmonary arteriovenous malformations and widely discrepant flow (80%) to the right lung leading to low flow in the left limb.The area-preserving, bifurcated Y-graft Fontan modification is technically feasible and shows excellent intermediate outcomes. Additional study is required to determine whether the advantages seen in the computational models will be realized in patients over the long-term, and to optimize patient selection for each of the various Fontan options now available.

Abstract

Pulmonary arterial hypertension (PAH) causes changes in the right ventricle (RV), affecting RV size and function, ultimately leading to death. These changes have been evaluated by cardiac MRI (CMR) in adults with PAH, but not in children. Using CMR in pediatric patients with PAH, we examined how RV size and function (1) compare to normal data, (2) change over time, and (3) compare to similar studies in the adult population. Data from two institutions were retrospectively reviewed. Subjects with PAH and a CMR were included. Baseline CMR variables (right and left ventricular end-diastolic and end-systolic volumes indexed for body surface area, and calculated stroke volume and ejection fraction) were compared to normative data and follow-up CMR data. Twenty-six subjects (15 female), age 2-16 (mean 11) years, with idiopathic PAH were included. All patients were on PAH medication, and 65% on prostacyclin therapy. The baseline 6-Minute Walk Distance (6MWD; 481 ± 137) was normal. RV volumes and ejection fraction were markedly abnormal compared to normal data (P < 0.001). Follow-up CMRs were analyzed in 15 patients. RV volumes and function and LV stroke volume showed no significant change over one year. Our pediatric patients with PAH have markedly abnormal right ventricles by CMR but have normal walk distances. The lack of change in CMR parameters over one year may represent a stable cohort and is different than similar studies in adults.

Abstract

The cardiac workload associated with various types of aortic obstruction was determined using computational fluid dynamic simulations.Computed tomography image data were collected from 4 patients with 4 distinct types of aortic arch obstructions and 4 controls. The categorization of arch hypoplasia corresponded to the "A, B, C" nomenclature of arch interruption; a type "D" was added to represent diffuse arch hypoplasia. Measurements of the vessel diameter were compared against the normal measurements to determine the degree of narrowing. Three-dimensional models were created for each patient, and additional models were created for type A and B hypoplasia to represent 25%, 50%, and 75% diameter narrowing. The boundary conditions for the computational simulations were chosen to achieve realistic flow and pressures in the control cases. The simulations were then repeated after changing the boundary conditions to represent a range of cardiac and vascular adaptations. The resulting cardiac workload was compared with the control cases.Of the 4 patients investigated, 1 had aortic coarctation and 3 had aortic hypoplasia. The cardiac workload of the patients with 25% narrowing type A and B hypoplasia was not appreciably different from that of the control. When comparing the different arch obstructions, 75% type A, 50% type B, and 50% type D hypoplasia required a greater workload increase than 75% coarctation.The present study has determined the hemodynamic significance of aortic arch obstruction using computational simulations to calculate the cardiac workload. These results suggest that all types of hypoplasia pose more of a workload challenge than coarctation with an equivalent degree of narrowing.

Abstract

Previous clinical studies in pulmonary arterial hypertension (PAH) have concentrated predominantly on distal pulmonary vascular resistance, its contribution to the disease process, and response to therapy. However, it is well known that biomechanical factors such as shear stress have an impact on endothelial health and dysfunction in other parts of the vasculature. This study tested the hypothesis that wall shear stress is reduced in the proximal pulmonary arteries of PAH patients with the belief that reduced shear stress may contribute to pulmonary endothelial cell dysfunction and as a result, PAH progression. A combined MRI and computational fluid dynamics (CFD) approach was used to construct subject-specific pulmonary artery models and quantify flow features and wall shear stress (WSS) in five PAH patients with moderate-to-severe disease and five age- and sex-matched controls. Three-dimensional model reconstruction showed PAH patients have significantly larger main, right, and left pulmonary artery diameters (3.5 ± 0.4 vs. 2.7 ± 0.1 cm, P = 0.01; 2.5 ± 0.4 vs. 1.9 ± 0.2 cm, P = 0.04; and 2.6 ± 0.4 vs. 2.0 ± 0.2 cm, P = 0.01, respectively), and lower cardiac output (3.7 ± 1.2 vs. 5.8 ± 0.6 L/min, P = 0.02.). CFD showed significantly lower time-averaged central pulmonary artery WSS in PAH patients compared to controls (4.3 ± 2.8 vs. 20.5 ± 4.0 dynes/cm(2), P = 0.0004). Distal WSS was not significantly different. A novel method of measuring WSS was utilized to demonstrate for the first time that WSS is altered in some patients with PAH. Using computational modeling in patient-specific models, WSS was found to be significantly lower in the proximal pulmonary arteries of PAH patients compared to controls. Reduced WSS in proximal pulmonary arteries may play a role in the pathogenesis and progression of PAH. This data may serve as a basis for future in vitro studies of, for example, effects of WSS on gene expression.

Abstract

Dose reduction techniques for computed tomography angiography (CTA) in children with cardiovascular diseases have the potential of reducing risks of radiation-induced cancer. To evaluate effectiveness of these techniques, both radiation dose and image quality must be compared. While clinically practical methods of estimating effective dose are available, there are no generally accepted metrics for the assessment of image quality in CTA. We introduce a measurable and reproducible image quality index, CTA QI. Using this index, along with calculated effective dose, we test the hypothesis that volume scan CTA delivers comparable image quality at substantially reduced radiation dose when compared to helical CTA. CTA QI is a measure of intraluminal contrast variation in three-dimensions, and it is calculated from standardized measurements of means and standard deviations of Hounsfield units in the thoracic descending aorta. From institutional database, 83 studies of CTA for thoracic cardiovascular diseases were retrospectively identified. CTA QI values were independently measured by two radiologists and compared using correlation. CTA QI and DLP-derived effective dose were compared for the following groups: non-cardiac gated wide-detector and helical CTA, ECG-synchronized retrospective wide-detector and helical CTA, ECG-synchronized wide detector retrospective and target technique CTA. Statistical significance was evaluated with the Student-t test. The correlations of CTA QI values between the radiologists were 0.83 and 0.92 for non-gated studies and ECG-synchronized studies respectively. Comparing non-gated volume scan CTA to helical CTA, there was a radiation dose reduction of 69% (P < 0.0001) without a significant change in CTA QI (1.4 ± 1.0 vs. 1.9 ± 1.4, P = 0.13). Comparing retrospective ECG-synchronized wide-detector CTA to helical CTA, there was a radiation dose reduction of 46% (P < 0.0001) with and improvement in CTA QI (1.0 ± 0.8 vs. 3.7 ± 3.4, P < 0.01). Comparing ECG-synchronized wide-detector target CTA to retrospective CTA, there was a radiation dose reduction of 68% (P < 0.0001, but at the cost of a significant reduction in CTA QI (2.0 ± 1.0 vs. 0.8 ± 0.4, P < 0.0044). CTA QI is a simple, reproducible metric of image quality suited for comparing CTA studies. Using this quality index, we establish that CTA performed with wide-detector scan techniques can yield substantially lower radiation dose without compromising diagnostic imaging quality. A wide-detector target technique can further reduce effective dose compared to wide-detector retrospective ECG-synchronization, but with a reduction in image quality.

Abstract

Contrast-enhanced cardiac MRA suffers from cardiac motion artifacts and often requires a breath-hold.This work develops and evaluates a blood pool contrast-enhanced combined respiratory- and ECG-triggered MRA method.An SPGR sequence was modified to enable combined cardiac and respiratory triggering on a 1.5-T scanner. Twenty-three consecutive children referred for pediatric heart disease receiving gadofosveset were recruited in HIPAA-compliant fashion with IRB approval and informed consent. Children underwent standard non-triggered contrast-enhanced MRA with or without suspended respiration. Additionally, a free-breathing-triggered MRA was acquired. Triggered and non-triggered studies were presented in blinded random order independently to two radiologists twice. Anatomical structure delineation was graded for each triggered and non-triggered acquisition and the visual quality on triggered MRA was compared directly to that on non-triggered MRA.Triggered images received higher scores from each radiologist for all anatomical structures on each of the two reading sessions (Wilcoxon rank sum test, P?0.05). In direct comparison, triggered images were preferred over non-triggered images for delineating cardiac structures, with most comparisons reaching statistical significance (binomial test, P?0.05).Combined cardiac and respiratory triggering, enabled by a blood pool contrast agent, improves delineation of most anatomical structures in pediatric cardiovascular MRA.

Abstract

Treatments for coarctation of the aorta (CoA) can alleviate blood pressure (BP) gradients (?), but long-term morbidity still exists that can be explained by altered indices of hemodynamics and biomechanics. We introduce a technique to increase our understanding of these indices for CoA under resting and nonresting conditions, quantify their contribution to morbidity, and evaluate treatment options. Patient-specific computational fluid dynamics (CFD) models were created from imaging and BP data for one normal and four CoA patients (moderate native CoA: ?12 mmHg, severe native CoA: ?25 mmHg and postoperative end-to-end and end-to-side patients: ?0 mmHg). Simulations incorporated vessel deformation, downstream vascular resistance and compliance. Indices including cyclic strain, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were quantified. Simulations replicated resting BP and blood flow data. BP during simulated exercise for the normal patient matched reported values. Greatest exercise-induced increases in systolic BP and mean and peak ?BP occurred for the moderate native CoA patient (SBP: 115 to 154 mmHg; mean and peak ?BP: 31 and 73 mmHg). Cyclic strain was elevated proximal to the coarctation for native CoA patients, but reduced throughout the aorta after treatment. A greater percentage of vessels was exposed to subnormal TAWSS or elevated OSI for CoA patients. Local patterns of these indices reported to correlate with atherosclerosis in normal patients were accentuated by CoA. These results apply CFD to a range of CoA patients for the first time and provide the foundation for future progress in this area.

Abstract

Atherosclerotic plaque in the descending thoracic aorta (dAo) is related to altered wall shear stress (WSS) for normal patients. Resection with end-to-end anastomosis (RWEA) is the gold standard for coarctation of the aorta (CoA) repair, but may lead to altered WSS indices that contribute to morbidity.Computational fluid dynamics (CFD) models were created from imaging and blood pressure data for control subjects and age- and gender-matched CoA patients treated by RWEA (four males, two females, 15 ± 8 years). CFD analysis incorporated downstream vascular resistance and compliance to generate blood flow velocity, time-averaged WSS (TAWSS), and oscillatory shear index (OSI) results. These indices were quantified longitudinally and circumferentially in the dAo, and several visualization methods were used to highlight regions of potential hemodynamic susceptibility.The total dAo area exposed to subnormal TAWSS and OSI was similar between groups, but several statistically significant local differences were revealed. Control subjects experienced left-handed rotating patterns of TAWSS and OSI down the dAo. TAWSS was elevated in CoA patients near the site of residual narrowings and OSI was elevated distally, particularly along the left dAo wall. Differences in WSS indices between groups were negligible more than 5?dAo diameters distal to the aortic arch.Localized differences in WSS indices within the dAo of CoA patients treated by RWEA suggest that plaque may form in unique locations influenced by the surgical repair. These regions can be visualized in familiar and intuitive ways allowing clinicians to track their contribution to morbidity in longitudinal studies.

Abstract

In this work, we examine the effects of stent-induced aortic stiffness on cardiac workload and blood pressure using computational fluid dynamic simulations.Treatment of aortic coarctation (CoA) consists of either open, surgical repair or angioplasty with or without stenting. Although stenting is a minimally invasive alternative to surgery, aortic stiffness increases in the stented section. Concern over this increased stiffness has long been argued to be detrimental to the overall vascular health of the patient.MR imaging was performed on a 15-year-old female with CoA. A 3D model of the large thoracic arteries was created, and the heart and downstream vasculature were represented by lumped parameter models at the model inlet and outlets, respectively. A deformable wall assumption was used in conjunction with variable wall properties and tissue support, and 3D velocity, pressure, and wall dynamics were computed. The lumped parameter values and wall properties were tuned to match the mean flow and aortic deformation as measured by MRI. The CoA was then virtually removed from the model representing an end-to-end surgical correction. In a second model, the repaired section was prescribed to be nearly rigid, representing stenting. All other variables remained the same.When compared to surgery, stenting resulted in clinically negligible increases in cardiac work (0.4%) and no change in mean blood pressure.This pilot study suggests CoA stenting may not affect cardiac work to any significant degree as is commonly believed in the clinical community.

Abstract

The biomechanical forces associated with blood flow have been shown to play a role in pulmonary vascular cell health and disease. Therefore, the quantification of human pulmonary artery hemodynamic conditions under resting and exercise states can be useful in investigating the physiology of disease development and treatment outcomes. In this study, a combined magnetic resonance imaging and computational fluid dynamics approach was used to quantify pulsatile flow fields, wall shear stress (WSS), oscillations in WSS (OSI), and energy efficiency in six subject-specific models of the human pulmonary vasculature with high spatial and temporal resolution. Averaging over all subjects, WSS was found to increase from 19.8±4.0 to 51.8±6.7 dynes/cm2, and OSI was found to decrease from 0.094±0.016 to 0.081±0.015 in the proximal pulmonary arteries between rest and exercise conditions (p<0.05). These findings demonstrate the localized, biomechanical effects of exercise. Furthermore, an average decrease of 10% in energy efficiency was noted between rest and exercise. These data indicate the amount of energy dissipation that typically occurs with exercise and may be useful in future surgical planning applications.

Abstract

Behcet's disease is a rare autoimmune disease characterized by oral and genital ulcers, and by multisystem disease, including arthritis, neurologic complications and vasculitis. Large-vessel and coronary artery aneurysms are often an indication for surgery, but the return of aneurysms, thrombosis, and the tendency to exhibit an exaggerated inflammatory response at puncture sites (pathergy) complicate surgical recovery. As such, cardiac transplantation, which requires atrial and large-vessel anastomoses, has not been reported in patients with Behcet's disease. We report the first orthotopic heart transplant with >1-year survival in a patient with Behcet's disease despite major complications. The investigators remain pessimistic about cardiac transplantation in patients with Behcet's disease until advances in preventing recurrent vascular pathology ensue.

Abstract

Moderate to severe hereditary spherocytosis (HS) is treated with splenectomy. However, total splenectomy leads to decreased immunologic function with the risk of overwhelming postsplenectomy sepsis. Splenic preservation is postulated as a method to avoid this potentially fatal complication. Although mainly performed through laparotomy, we report our experience with a laparoscopic approach to partial splenectomy for HS.A retrospective review was conducted on 9 laparoscopic partial splenectomies performed for HS at our institution. Follow-up was from 1 to 3.5 years. Data included preoperative and postoperative hemoglobin, absolute reticulocyte count, splenic size, operative time, complications, and length of stay.All patients successfully underwent laparoscopic partial splenectomy with a radiologically determined upper-pole remnant of 10% to 30% and preservation of the blood supply through the upper short gastric arteries. The mean preoperative spleen length was 13 cm. Mean hospital stay was 3.6 days (range, 1-6 days). There was 1 intraoperative complication (a small bowel tear during spleen extraction) and 2 minor postoperative complications (ileus and wound infection). One patient underwent completion total splenectomy 2 years after partial splenectomy.Laparoscopic partial splenectomy is a feasible and effective procedure that addresses the hematologic consequences of HS while retaining a portion of functional spleen, in addition to conferring the advantages of laparoscopy.

Abstract

Heterotaxy with polysplenia is associated with many cardiovascular anomalies including the occasional occurrence of congenital extrahepatic portosystemic shunts (CEPS). Missing this anomaly can lead to inappropriate and ineffective therapy.To emphasize the importance and associated anatomy of CEPS in conjunction with heterotaxy with polysplenia.Review of three young children who presented with cyanosis and pulmonary hypertension without a cardiac etiology. They were known (1) or discovered (2) to have heterotaxy with polysplenia.There was absence of the intrahepatic inferior vena cava (IVC) with azygos or hemiazygos continuation in all three cases. In spite of normal liver function, they were discovered to have large portosystemic shunts, splenorenal in location, along with diffuse peripheral pulmonary arterial dilatation suggestive of CEPS (Abernethy malformation) with hepatopulmonary or, more accurately, portopulmonary syndrome. All CEPS were ipsilateral to the spleens. Patency of the portal veins in these cases allowed for percutaneous shunt closure with resolution of cyanosis.CEPS is associated with heterotaxy with polysplenia and can be symptomatic because of pulmonary arteriovenous (AV) shunting. Portal and hepatic vein patency are critical for determining feasibility of CEPS closure.

Abstract

To compare generalized autocalibrating partially parallel acquisitions (GRAPPA), modified sensitivity encoding (mSENSE), and SENSE in phase-contrast magnetic resonance imaging (PC-MRI) applications.Aliasing of the torso can occur in PC-MRI applications. If the data are further undersampled for parallel imaging, SENSE can be problematic in correctly unaliasing signals due to coil sensitivity maps that do not match that of the aliased volume. Here, a method for estimating coil sensitivities in flow applications is described. Normal volunteers (n = 5) were scanned on a 1.5 T MRI scanner and underwent PC-MRI scans using GRAPPA, mSENSE, SENSE, and conventional PC-MRI acquisitions. Peak velocity and flow through the aorta and pulmonary artery were evaluated.Bland-Altman statistics for flow in the aorta and pulmonary artery acquired with mSENSE and GRAPPA methods (R = 2 and R = 3 cases) have comparable mean differences to flow acquired with conventional PC-MRI. GRAPPA and mSENSE PC-MRI have more robust measurements than SENSE when there is aliasing artifact caused by insufficient coil sensitivity maps. For peak velocity, there are no considerable differences among the mSENSE, GRAPPA, and SENSE reconstructions and are comparable to conventional PC-MRI.Flow measurements of images reconstructed with autocalibration techniques have comparable agreement with conventional PC-MRI and provide robust measurements in the presence of wraparound.

Abstract

Despite an abundance of prior Fontan simulation articles, there have been relatively few clinical advances that are a direct result of computational methods. We address a few key limitations of previous Fontan simulations as a step towards increasing clinical relevance. Previous simulations have been limited in scope because they have primarily focused on a single energy loss parameter. We present a multi-parameter approach to Fontan modeling that establishes a platform for clinical decision making and comprehensive evaluation of proposed interventions.Time-dependent, 3-D blood flow simulations were performed on six patient-specific Fontan models. Key modeling advances include detailed pulmonary anatomy, catheterization-derived pressures, and MRI-derived flow with respiration. The following performance parameters were used to rank patients at rest and simulated exercise from best to worst performing: energy efficiency, inferior and superior vena cava (IVC, SVC) pressures, wall shear stress, and IVC flow distribution.Simulated pressures were well matched to catheterization data, but low Fontan pressure did not correlate with high efficiency. Efficiency varied from 74% to 96% at rest, and from 63% to 91% with exercise. Distribution of IVC flow ranged from 88%/12% (LPA/RPA) to 53%/47%. A "transcatheter" virtual intervention demonstrates the utility of computation in evaluating interventional strategies, and is shown to result in increased energy efficiency.A multiparameter approach demonstrates that each parameter results in a different ranking of Fontan performance. Ranking patients using energy efficiency does not correlate with the ranking using other parameters of presumed clinical importance. As such, current simulation methods that evaluate energy dissipation alone are not sufficient for a comprehensive evaluation of new Fontan designs.

Abstract

Whether congenital or acquired, timely recognition and management of disease is imperative, as hemodynamic alterations in blood flow, tissue perfusion, and cellular oxygenation can have profound effects on organ function, growth and development, and quality of life for the pediatric patient. Ensuring safe computed tomographic angiography (CTA) practice and "gentle" pediatric imaging requires the cardiovascular imager to have sound understanding of CTA advantages, limitations, and appropriate indications as well as strong working knowledge of acquisition principles and image post processing. From this vantage point, CTA can be used as a useful adjunct along with the other modalities. This article presents a summary of dose reduction CTA methodologies along with techniques the authors have employed in clinical practice to achieve low-dose and ultralow-dose exposure in pediatric CTA. CTA technical principles are discussed with an emphasis on the low-dose methodologies and safe contrast medium delivery strategies. Recommended parameters for currently available multidetector-row computed tomography scanners are summarized alongside recommended radiation and contrast medium parameters. In the second part of the article an overview of pediatric CTA clinical applications is presented, illustrating low-dose and ultra-low dose techniques, with an emphasis on the specific protocols.

Abstract

The objective of this work is to evaluate the hemodynamic performance of a new Y-graft modification of the extracardiac conduit Fontan operation. The performance of the Y-graft design is compared to two designs used in current practice: a t-junction connection of the venae cavae and an offset between the inferior and superior venae cavae.The proposed design replaces the current tube grafts used to connect the inferior vena cava to the pulmonary arteries with a Y-shaped graft. Y-graft hemodynamics were evaluated at rest and during exercise with a patient-specific model from magnetic resonance imaging data together with computational fluid dynamics. Four clinically motivated performance measures were examined: Fontan pressures, energy efficiency, inferior vena cava flow distribution, and wall shear stress. Two variants of the Y-graft were evaluated: an "off-the-shelf" graft with 9-mm branches and an "area-preserving" graft with 12-mm branches.Energy efficiency of the 12-mm Y-graft was higher than all other models at rest and during exercise, and the reduction in efficiency from rest to exercise was improved by 38%. Both Y-graft designs reduced superior vena cava pressures during exercise by as much as 5 mm Hg. The Y-graft more equally distributed the inferior vena cava flow to both lungs, whereas the offset design skewed 70% of the flow to the left lung. The 12-mm graft resulted in slightly larger regions of low wall shear stress than other models; however, minimum shear stress values were similar.The area-preserving 12-mm Y-graft is a promising modification of the Fontan procedure that should be clinically evaluated. Further work is needed to correlate our performance metrics with clinical outcomes, including exercise intolerance, incidence of protein-losing enteropathy, and thrombus formation.

Abstract

Cardiac magnetic resonance imaging (MRI) and computed tomography (CT) are imaging modalities increasingly used in the diagnosis and management of structural heart disease. They are powerful imaging tools that have individual strengths and weaknesses. Rational choice between MRI and CT should be based on a sound understanding of these issues. Management guidelines that incorporate the use of MRI and CT are currently being developed, and their utilizations are expected to grow rapidly in the future.

Abstract

We sought to identify and characterize the abnormal vascular structures responsible for pulmonary arteriovenous shunting following the Glenn cavopulmonary shunt. Superior cavopulmonary shunt is commonly performed as part of the staged pathway to total cavopulmonary shunt to treat univentricular forms of congenital heart disease, however, clinically significant pulmonary arteriovenous malformations develop in some patients after the procedure. The causes of pulmonary arteriovenous malformations and other pulmonary vascular changes that occur after cavopulmonary shunt are not known. Using a juvenile lamb model of superior cavopulmonary anastomosis that reliably produces pulmonary arteriovenous malformations, we performed echocardiography and morphological analyses to determine the anatomic site of shunting and to identify the vascular structures involved. Pulmonary arteriovenous shunting was identified by contrast echocardiography in all surviving animals (n = 40) following superior cavopulmonary anastomosis. Pulmonary vascular corrosion casts revealed abnormal tortuous vessels joining pulmonary arteries and veins in cavopulmonary shunt animals but not control animals. In conclusion, unusual channels that bridged pulmonary arteries and veins were identified. These may represent the vascular structures responsible for arteriovenous shunting following the classic Glenn cavopulmonary shunt. Detailed analysis of these structures may elucidate factors responsible for their development.

Abstract

Cardiac computed tomography (CT) is commonly used to visualize left atrial (LA) anatomy for ablation of atrial fibrillation. We have developed a new imaging technique that allows acquisition and visualization of three-dimensional (3D) cardiac images in the catheter lab.We sought to compare LA and pulmonary vein (PV) dimensions acquired using gated multisweep rotational fluoroscopy (C-arm CT) system and multislice computed tomography (MSCT) in an in vivo porcine model.A Siemens AXIOM Artis dTA C-arm system (Siemens AG, Medical Solutions) was modified to allow acquisition of four bidirectional sweeps during synchronized acquisition of the electrocardiogram signal to allow retrospective gating. C-arm CT image volumes were then reconstructed. Gated MSCT (SOMATOM Sensation 16 and 64, Siemens AG, Medical Solutions) and C-arm CT images were acquired in six animals. The two main PV diameters were measured in orthogonal axes. LA volumes were calculated. C-arm CT measurements were compared with the MSCT measurements.The average PV diameters using the C-arm CT were 2.24 x 1.35 cm, versus 2.27 x 1.38 cm for CT. The average difference was 0.034 cm (1.9%) between the C-arm CT and standard CT. The average LA volume using MSCT was 49.1 +/- 12.7 cm(3), as compared with 51.0 +/- 8.7 cm(3) obtained by the C-arm CT. The average difference between the C-arm CT and the MSCT was 1.9 cm(3) (3.7%). There were no significant differences in either the PV or LA measurements.Visualization of 3D cardiac anatomy during ablation procedures is possible and highly accurate. The 3D cardiac reconstructions acquired during ablation procedures will be valuable for procedural planning and guidance.

Abstract

Cardiac MRI and CT are imaging modalities increasingly employed in the diagnosis and management of structural heart disease. They are powerful imaging tools that have individual strengths and weaknesses. Rational choice between MRI and CT should be based on a sound understanding of these issues. Management guidelines that incorporate the use of MRI and CT are currently being developed, and their utilizations are expected to grow rapidly in the future.

Abstract

Conventional sensitivity encoding (SENSE) reconstruction is based on equations in the complex domain. However, for many MRI applications only the magnitude is relevant. If there exists an estimate of the underlying phase information, a magnitude-only phase-constrained reconstruction can help to improve the conditioning of the SENSE reconstruction problem. Consequently, this reduces g-factor-related noise enhancement. In previous attempts at phase-constrained SENSE reconstruction, image quality was hampered by strong aliasing artifacts resulting from inadequate phase estimates and high sensitivity to phase errors. If a full-resolution phase image is used, a significant reduction in aliasing errors and better noise properties compared to SENSE can be obtained. An iterative scheme that improves the phase estimate to better approximate the phase is presented. The mathematical framework of the new approach is provided together with comparisons of conventional SENSE, phase-constrained SENSE, and the new phase-refinement method. Both theory and experimental verification demonstrate significantly better noise performance at high reduction factors, i.e., close to the theoretical limit. For applications that need only magnitude data, an iterative phase-constrained SENSE reconstruction can provide substantial SNR improvement over SENSE reconstruction and less artifacts than phase-constrained SENSE.

Abstract

Phase-contrast (PC) magnetic resonance imaging (MRI) technique has important clinical applications in blood flow quantification and pressure gradient estimation by velocity measurement. Parallel imaging using sensitivity encoding (SENSE) may substantially reduce scan time. We demonstrate the utility of PC-MRI measurements accelerated by SENSE under clinical conditions.Accuracy and repeatability of a SENSE-PC implementation was evaluated by comparison with a commercial PC sequence with five normal volunteers. Twenty-six patients were then scanned with SENSE-PC at reduction factors (R = 1, 2, and 3). Blood flow and peak velocity were measured in the aorta and pulmonary trunk in 16 patients and peak velocity was measured at the coarctation of 10 patients. Quantitative flow, shunt ratio, and peak velocity measurements obtained with different reduction factors were compared using correlation, linear regression, and Bland-Altman statistics. All studies were approved by an Institutional Review Board, and informed consent was acquired from all subjects.The correlation coefficients for all comparisons were >0.962 and with high statistical significance (P < .01). Linear regression slopes ranged between 0.96 and 1.11 for flow and 0.88 to 1.05 for peak velocity. For flow, the Bland-Altman statistics yielded a total mean difference ranging from -0.02 to 0.05) L/minute with 2 standard of deviation limits ranging from -0.52 to 0.75 L/minute. For peak velocity, the total mean difference ranged from -0.10 to -0.004) milliseconds with 2-SD limits ranging from -0.062 to 0.46 milliseconds. R = 3 to R = 1 comparisons had greater 2-SD limits than R = 2 to R = 1 comparisons.SENSE PC-MRI measurements for flow and pressure gradient estimation were comparable to conventional PC-MRI.

Abstract

We describe echocardiography and computerized tomographic imaging findings in the two subtypes of fifth aortic arch in infants. In the first form, the fifth aortic arch creates a systemic to systemic connection extending from the ascending to the descending aorta. When this form appears in isolation, it does not cause hemodynamic disturbance, although associated cardiac lesions, such as aortic coarctation or interruption and patent ductus arteriosus, may influence the clinical presentation. In the second form the fifth aortic arch connects the systemic and pulmonary circulations from persistent connections between the embryological fifth and sixth arches, which may cause significant hemodynamic disturbance from left to right shunting. Although this form has been associated with a wide array of congenital cardiac lesions, this is the first description of 5th aortic arch in association with atrioventricular septal defect and double outlet right ventricle.

Abstract

Congenital heart defects with a single functional ventricle, such as hypoplastic left heart syndrome and tricuspid atresia, require a staged surgical approach to separate the systemic and pulmonary circulations. Ultimately, the venous or pulmonary side of the heart is bypassed by directly connecting the vena cava to the pulmonary arteries with a modified t-shaped junction. The Fontan procedure (total cavopulmonary connection, TCPC) completes this process of separation. To date, computational fluid dynamics (CFD) simulations in this low pressure, passive flow, intrathoracic system have neglected the presumed important effects of respiration on physiology and higher "stress" states such as with exercise have never been considered. We hypothesize that incorporating effects of respiration and exercise would provide more realistic estimates of TCPC performance. Time-dependent, 3D blood flow simulations are performed by a custom finite element solver for two patient-specific Fontan models with a novel respiration model, developed to generate physiologic time-varying flow conditions. Blood flow features, pressure, and energy efficiency are analyzed at rest and with increasing flow rates to simulate exercise conditions. The simulations produce realistic pressure and flow data, comparable to that measured by catheterization and echocardiography, and demonstrate substantial increases in energy dissipation (i.e. decreased performance) with exercise and respiration due to increasing intensity of small scale vortices in the flow. As would be expected, these changes are highly dependent on patient-specific anatomy and Fontan geometry. We propose that respiration and exercise should be incorporated into TCPC CFD simulations to provide increasingly realistic evaluations of TCPC performance.

Abstract

Multi-detector-row computed tomography (MDCT) enables rapid, noninvasive, high-resolution, and three-dimensional imaging of pediatric vascular diseases. In this paper, we explore the adaptation of the MDCT angiographic principles to pediatric patients for vascular diseases of the abdomen, pelvis, and extremities. Special emphasis is placed on the practical aspects of how to perform these studies. Optimizations of scan parameters, contrast medium usage, radiation dose, and three-dimensional image processing are discussed in detail. We provide practical guidance on how to choose between MR angiography and CT angiography. Finally, we review important pediatric vascular diseases, categorized into traumatic injuries, inherited vascular diseases, congenital vascular diseases, vasculitides, and surgical planning and assessment. In each category, we discuss how CT angiography can be tailored to maximize its clinical benefits.

Abstract

Multidetector-row computed tomography (MDCT) is an essential diagnostic modality for many clinical algorithms. This is particularly true with regard to the evaluation of cardiovascular disease. As a result of increased image acquisition speed, improved spatial resolution, and greater scan volume, MDCT angiography (computed tomography angiography [CTA]) has become an excellent noninvasive imaging technique, replacing intra-arterial digital subtraction angiography for most vascular territories. The clinical success of CTA depends on precise synchronization of image acquisition with optimal vascular enhancement. As technology continuously evolves, however, this task can be challenging. It remains important to have a fundamental knowledge of the principles behind technical parameters and contrast medium administration. This article reviews these essential principles, followed by an overview of current clinical applications.

Abstract

An analysis of thoracic aortic blood flow in normal subjects and patients with aortic pathologic findings is presented. Various visualization tools were used to analyze blood flow patterns within a single 3-component velocity volumetric acquisition of the entire thoracic aortaTime-resolved, 3-dimensional phase-contrast magnetic resonance imaging (3D CINE PC MRI) was employed to obtain complete spatial and temporal coverage of the entire thoracic aorta combined with spatially registered 3-directional pulsatile blood flow velocities. Three-dimensional visualization tools, including time-resolved velocity vector fields reformatted to arbitrary 2-dimensional cut planes, 3D streamlines, and time-resolved 3D particle traces, were applied in a study with 10 normal volunteers. Results from 4 patient examinations with similar scan prescriptions to those of the volunteer scans are presented to illustrate flow features associated with common pathologic findings in the thoracic aorta.Previously reported blood flow patterns in the thoracic aorta, including right-handed helical outflow, late systolic retrograde flow, and accelerated passage through the aortic valve plane, were visualized in all volunteers. The effects of thoracic aortic disease on spatial and temporal blood flow patterns are illustrated in clinical cases, including ascending aortic aneurysms, aortic regurgitation, and aortic dissection.Time-resolved 3D velocity mapping was successfully applied in a study of 10 healthy volunteers and 4 patients with documented aortic pathologic findings and has proven to be a reliable tool for analysis and visualization of normal characteristic as well as pathologic flow features within the entire thoracic aorta.

Abstract

With the advent of therapies aimed at young patients with cystic fibrosis, who have mildly reduced pulmonary function, the need for improved outcome measures that discriminate treatment effects has become important. Pulmonary function measurements or chest high-resolution computed tomography (HRCT) scores have been separately used to assess interventions. We evaluated these modalities separately and together during a treatment study to develop a more sensitive outcome measure. In a 1-year trial, 25 children randomized either to daily Pulmozyme or to normal saline aerosol were evaluated at randomization and at 3 and 12 months. Outcome variables were pulmonary function test (PFT) results, a global HRCT score, and a composite score incorporating PFTs and HRCT scoring. Regression analyses with generalized estimating equations permitted estimation of the difference in treatment effect between groups over time for each outcome. The largest difference in treatment effects observed at 12 months, measured by the percentage change from baseline, were with the composite total and maximal CT/PFT scores (35.4 and 30.4%), compared with mean forced expiratory flow during the middle half of the FVC (FEF25-75%) (13.0%) and total and maximal global HRCT scores (6.2%, 7.2%). The composite total and maximal CT/PFT scores were the most sensitive outcome measures for discriminating a treatment effect in children with cystic fibrosis with normal or mildly reduced pulmonary function during a 1-year trial of Pulmozyme.

Abstract

To automatically derive the degree of air trapping in mild cystic fibrosis (CF) disease from high-resolution CT (HRCT) data, and to evaluate the discriminating power of the measurement.The data consist of six pairs of anatomically matched tomographic slices, obtained during breath-holding in triggered HRCT acquisitions. The pairs consist of an inspiratory slice, at > or = 95% of slow vital capacity, and an expiratory slice at near residual volume (nRV). The subjects are 25 patients with mild CF and 10 age-matched, normal control subjects.Lung segmentation is automatic. The limits defining air trapping in the expiratory slices are determined by the distribution of densities in the expanded lung. They are modulated by density changes between expiration and inspiration. Air trapping defects consist of contiguous low-density voxels. The difference between patients and control subjects was evaluated in comparison to pulmonary function test (PFT) results and lung density distribution descriptors (global density descriptors).In mild CF, air trapping does not correlate with global PFT results, except for the ratio of residual volume (RV) to total lung capacity (TLC); however, the size of air trapping defects was the best discriminator between patients and control subjects (p < 0.005). Of PFT results, only RV/TLC reached significance at p < 0.05. The global density descriptors reached near significance in the nRV images only.Air trapping defined as defect size and measured in an objective automated manner is a powerful discriminator for mild CF.

Abstract

To demonstrate the feasibility of a four-dimensional phase contrast (PC) technique that permits spatial and temporal coverage of an entire three-dimensional volume, to quantitatively validate its accuracy against an established time resolved two-dimensional PC technique to explore advantages of the approach with regard to the four-dimensional nature of the data.Time-resolved, three-dimensional anatomical images were generated simultaneously with registered three-directional velocity vector fields. Improvements compared to prior methods include retrospectively gated and respiratory compensated image acquisition, interleaved flow encoding with freely selectable velocity encoding (venc) along each spatial direction, and flexible trade-off between temporal resolution and total acquisition time.The implementation was validated against established two-dimensional PC techniques using a well-defined phantom, and successfully applied in volunteer and patient examinations. Human studies were performed after contrast administration in order to compensate for loss of in-flow enhancement in the four-dimensional approach.Advantages of the four-dimensional approach include the complete spatial and temporal coverage of the cardiovascular region of interest and the ability to obtain high spatial resolution in all three dimensions with higher signal-to-noise ratio compared to two-dimensional methods at the same resolution. In addition, the four-dimensional nature of the data offers a variety of image processing options, such as magnitude and velocity multi-planar reformation, three-directional vector field plots, and velocity profiles mapped onto selected planes of interest.

Abstract

In planning operations for patients with cardiovascular disease, vascular surgeons rely on their training, past experiences with patients with similar conditions, and diagnostic imaging data. However, variability in patient anatomy and physiology makes it difficult to quantitatively predict the surgical outcome for a specific patient a priori. We have developed a simulation-based medical planning system that utilizes three-dimensional finite-element analysis methods and patient-specific anatomic and physiologic information to predict changes in blood flow resulting from surgical bypass procedures. In order to apply these computational methods, they must be validated against direct experimental measurements. In this study, we compared in vivo flow measurements obtained using magnetic resonance imaging techniques to calculated flow values predicted using our analysis methods in thoraco-thoraco aortic bypass procedures in eight pigs. Predicted average flow rates and flow rate waveforms were compared for two locations. The predicted and measured waveforms had similar shapes and amplitudes, while flow distribution predictions were within 10.6% of the experimental data. The average absolute difference in the bypass-to-inlet blood flow ratio was 5.4 +/- 2.8%. For the aorta-to-inlet blood flow ratio, the average absolute difference was 6.0 +/- 3.3%.

Abstract

Takayasu's arteritis (TA) has a mortality rate of up to 40% in children. Because the clinical presentation of TA is often non-specific, accurate and prompt diagnosis depends on a high degree of awareness and appropriate laboratory and imaging studies.To examine the use of advanced magnetic resonance imaging (MRI) in evaluating, gauging activity, and following the complications of TA.T1 weighted, T2 weighted, contrast enhanced MR images, and MR angiograms of the chest and abdomen were obtained in three children (age range 11-14 years). The MRI studies confirmed the diagnosis of active TA and were repeated to evaluate response to treatment. Two patients showed complete resolution of lesions found on MRI at six and 12 months' follow up, while the third patient showed no significant improvement.MRI can be used to help establish the initial diagnosis of TA in children, and it can also be used to monitor disease activity and to guide treatment.

Abstract

The purpose of this study was to determine the accuracy of a multiphasic gadolinium-enhanced three-dimensional (3D) fast spoiled gradient-recalled echo sequence alone in the detection and characterization of focal liver lesions compared with a comprehensive liver evaluation using multiphasic gadolinium-enhanced 3D fast spoiled gradient-recalled echo, T1-weighted, and fat-suppressed fast spin-echo T2-weighted sequences.A retrospective review of abdominal MR imaging examinations in 61 patients was performed. All MR examinations included unenhanced spin-echo T1-weighted, unenhanced fat-suppressed fast spin-echo T2-weighted, and multiphasic gadolinium-enhanced 3D fast spoiled gradient-recalled echo sequences obtained during successive breath-holds. The liver was evaluated for focal lesions first with the 3D spoiled gradient-recalled echo sequences and then, during a separate sitting, with the T1- and T2-weighted sequences. The usefulness of each sequence in the detection and characterization of lesions was recorded. The gold standard for lesion detection and characterization was all three imaging sequences reviewed together.A total of 114 focal liver lesions were identified, 54 of which were simple cysts. The 3D spoiled gradient-recalled echo sequence alone detected 92 (81%) of the 114 lesions, and the T1- and T2-weighted sequences detected 95 (83%) of the 114 lesions. Of the 60 lesions that were not simple cysts, the 3D spoiled gradient-recalled echo sequence alone detected 58 (97%), and T1- and T2-weighted sequences detected 51 (85%). In 24% of the patients with lesions, the T1- and T2-weighted sequences were found to be helpful for the characterization of lesions.A multiphasic contrast-enhanced 3D fast spoiled gradient-recalled echo sequence alone detects most of the clinically relevant focal liver lesions. Additional liver examination using both unenhanced T1- and T2-weighted sequences is helpful for lesion characterization but increases the detection rate only minimally.

Abstract

The authors tested whether noninvasive magnetic resonance (MR) oximetry is accurate in the in vivo measurement of oxygen saturation in a stroma-free, hemoglobin-based oxygen carrier (HBOC).A central venous catheter was placed in the inferior vena cava (IVC) of 10 New Zealand white rabbits (weight range, 2.5-3.2 kg). Each rabbit underwent removal of 20% of blood volume followed by resuscitation with 10 mL/kg of bovine HBOC-200. Oxygen saturation of the blood mixture was measured in vivo at the IVC with MR oximetry, with separate in vitro calibration for each animal. Blood drawn from the IVC was measured with ex vivo oximetry, which was used as the standard of reference. The in vivo and ex vivo measurements were compared.There was no significant difference (P > .1) between measurements obtained with MR oximetry and ex vivo oximetry. The results with in vivo MR oximetry demonstrated excellent correlation with those from ex vivo oximetry (r = 0.99) over a wide range of physiologic oxygen saturation values (16.7%-74.9%) in venous blood.Noninvasive in vivo MR measurement of oxygen saturation is valid for whole blood mixed with stroma-free hemoglobin. Therefore, MR oximetry may be clinically useful for assessing the oxygenation status in patients resuscitated with a HBOC.

Abstract

In the past few years, tremendous advances have been made in the fields of magnetic resonance imaging, computed tomography and ultrasonography. These include the development of novel contrast agents and new approaches to image acquisition and processing. This review provides an overview of the state-of-the-art of imaging investigation of focal hepatic lesions and highlights some of the most exciting emerging technologies.

Abstract

Acute mesenteric ischemia is a lethal disease that lacks a noninvasive diagnostic test. We evaluated the abilities of contrast-enhanced MR angiography, MR oximetry, and real-time interactive MR imaging to diagnose segmental mesenteric ischemia in a porcine model.Segmental mesenteric ischemia was created by subselective Gelfoam embolization of the mesenteric circulation in eight pigs. Conventional digital subtraction angiography (DSA), MR oximetry, and real-time interactive MR imaging of the small bowel were performed before and after embolization. Changes in the perfusion pattern seen on DSA established the regions of true ischemia. Postembolization DSA and MR angiography were compared with this gold standard.Both MR angiography and DSA had high sensitivity (91% and 100%, respectively) for detecting ischemic regions. The difference was not statistically significant (p > .2). MR angiography yielded lower specificity than DSA (80% and 90%, respectively; p < .01). After embolization, the oxygen saturation in the superior mesenteric vein (SMV) dropped significantly (p < .005). After embolization, the SMV also showed oxygen saturation significantly lower than that in the inferior vena cava (p < .005). In two of the animals, segmental hypomotility of the small bowel was observed.MR oximetry is capable of detecting oxygen desaturation caused by segmental ischemia. A loss of oxygen saturation in the SMV relative to that in the inferior vena cava provides a convenient marker of mesenteric ischemia. Contrast-enhanced MR angiography has sensitivity and specificity approaching those of DSA. Both MR techniques hold promise for the detection of acute mesenteric ischemia.

Abstract

In the past few years, tremendous advances have been made in the fields of ultrasound, computed tomography, magnetic resonance imaging and contrast agent development. The purpose of this article is to highlight the important developments in imaging techniques that can be used for detection and characterization of focal hepatic lesions.

Abstract

In a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The nonideal behavior of this amplifier distorts a selective-excitation pulse, and this distortion in turn degrades the slice profile. We have found two types of nonideal behavior particularly troublesome: nonlinearity and incidental phase modulation. One of their effects is the introduction of an unwanted "skirt" in the out-of-slice region of a slice profile. We present an effective method of correction in which a selective-excitation pulse is prewarped to compensate for the distortion.